The automated handling of large numbers of liquid samples is necessary in many pharmaceutical and chemical applications, such as drug packaging and testing of various types of liquids including blood reagents and laboratory assays. In such applications, the volume of the liquid in a large number of sample containers must be measured accurately on a high-speed basis. The samples are often of micro-liter size in test tubes or vials having restricted size openings.
In a manual, or semi-automated filling process, the liquid is aspirated into the containers using a pipetting technique and a measurement is made of the liquid level by inserting a probe into the container until it contacts the liquid. This is highly undesirable, particularly when the samples are contaminated, contain toxic liquids, or the sterility of the newly packaged product is to be preserved. Also, the step of making the measurement is relatively slow and sometimes produces inaccuracies.